1. Field of the Invention
The present invention relates to apparatus for drawing glass tubing, and particularly to an apparatus for preparing micropipettes from quartz tubing.
2. Description of the Related Art
Micropipettes are a commonly used item of glassware in the biology laboratory. Sharp micropipettes are used to record electrical activity inside the cell. Injection micropipettes are used to transfer materials into and out of the cell through the cell membrane. Blunt patch pipettes are used to record electrical activity within a patch of the cell membrane or to record the electrical activity of the entire cell. Micropipettes are commonly made from borosilicate or aluminosilicate glass due to their low cost and comparatively easier fabrication. Quartz or fused silicate glass is harder and tougher than borosilicate or aluminosilicate glass. It is very desirable to have micropipettes made from quartz for certain applications, such as impaling cells underneath a deep tissue or wrapped by a layer of tough connective tissue; injections requiring a large diameter and relatively strong tip; and for low noise single ion channel recording because of the low electronic noise characteristic of the quartz glass.
There are, however, several problems encountered in drawing quartz glass for the preparation of micropipettes. Conventional glass pullers use electrically heated filaments of platinum or chromium, which are not effective in pulling quartz glass at the 1600.degree. C. temperature at which quartz softens. Tungsten, molybdenum or graphite filaments can withstand the high temperature, but require an inert gas environment to prevent oxidation of the filaments. Electric arc and several types of gas flames can melt quartz capillary tubes, but it is not as easy to control the intensity of the heat. Laser beams overcome many of these disadvantages. However, laser beam radiation heats the tubing from the inside out, so that when the quartz tubing is pulled, the ratio of the outside diameter to the inside diameter of the tubing diminishes, with the inside thinning more rapidly than the outside, being most pronounced at the tip of the micropipette and with multicycle pulling.
The present invention resolves the problems of the prior art by providing an apparatus for preparing quartz micropipettes utilizing a micropipette puller with heat supplied by miniature torches fueled by a propane-oxygen mixture with a sensor under computer control to determine when the quartz has softened sufficiently, automatically shutting down the heat source and pulling the tubing to produce symmetrical micropipettes with tips having an outside diameter to inside diameter ratio substantially close to the corresponding ratio of the original capillary tubing.
U.S. Pat. No. 4,530,712, issued Jul. 23, 1985 to J. D. Kopf, describes an apparatus for drawing micropipettes less than ten microns in diameter having a fixed clamp and a slidable clamp which moves vertically downward by gravity to stretch glass tubing softened by heat provided by a platinum filament, and an optical switch to shut off power to the heater when the tubing has been stretched the desired distance. U.S. Pat. No. 4,818,266, issued Apr. 4, 1989 to Sachs, et al., teaches an apparatus and method for pulling glass tubing using a stationary head stock and moveable tailstock, the stocks having the chuck and collet of a motor mounted in journals in the stock, the collets grasping opposite ends of glass tubing. The tubing is heated electrically while the motors rotate the tubing in the same direction and at the same speed, the tailstock being pulled when the glass softens while the heating element is simultaneously moved one-half the distance the tailstock is moved in order to maintain uniform heating.
U.S. Pat. No. 4,600,424, issued Jul. 15, 1986 to D. G. Flaming, shows a method of making ultrafine micropipettes using heat applied to a length of capillary tubing with the weight of a solenoid plunger suspended from one end of the tubing and a velocity monitor in the length of cable between the end of the tubing and the solenoid plunger. The heating is stopped and the tubing cooled with nitrogen when the velocity reaches a predetermined speed. U.S. Pat. No. 4,869,745, issued Sep. 26, 1989, also to D. G. Flaming, describes a micropipette puller having jaws at the end of puller bars grasping opposite ends of a length of capillary tubing. The puller bars roll along roller bearings and are pulled by cables routed over pulleys and pulled slightly by the weight of a solenoid and more strongly by the plunger of the solenoid under computer control when the tubing is sufficiently softened. Heat is applied to the middle of the tubing by a laser beam redirected either by reflection in a mirror or refraction through a prism, the mirror or prism being oscillated by a stepper motor to heat the tube uniformly.
U.S. Pat. No. 5,181,948, issued Jan. 26, 1993 to J. H. Belgum, discloses essentially the same device as the second Flaming patent, but the size of the laser beam is controlled by directing the beam through an aperture with adjustable shutters, or through an aperture of fixed size which is removable and replaceable by smaller or larger size apertures.
German Patent 3,106,045, published May 6, 1982, shows a method and apparatus for the production of small capillary tubes from glass or quartz, including an electric motor which rotates glass tubing, heating the tubing in the middle and pulling the tubing apart as it softens by means of permanent magnets arranged with their poles repelling each other, one of the magnets being mounted on a leaf spring which pulls a shaft connected to one end of the tubing. U.S. Pat. No. 2,987,372, issued Jun. 6, 1961 to Olt, et al., describes a method of making spools of microtubing from a wider diameter quartz tubing which utilizes oxygen and a propane torch to heat the tubing.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus an apparatus for preparing quartz micropipettes solving the aforementioned problems is desired.